(h)arq for semi-persistent scheduling

ABSTRACT

A radio communications link is established between radio stations, and a semi-persistent radio resource is allocated to support data transmission over the communications link. The semi-persistent radio resource is associated with a corresponding automatic repeat request (ARQ) process identifier. Non-limiting examples of a semi-persistent radio resource include a regularly scheduled transmission time interval, frame, subframe, or time slot during which to transmit a data unit over the radio interface. Retransmission is requested of a data unit transmitted using the semi-persistent radio resource. The ARQ process identifier associated with the semi-persistent resource is used to match a retransmission of a data unit dynamically scheduled on the communications link with the requested data unit retransmission. In a preferred example embodiment, the ARQ process identifier is a hybrid ARQ (HARQ) process, where a retransmitted data unit is combined with a previously-received version of the data unit.

TECHNICAL FIELD

The technical field relates to a mobile radio communications system andto such systems where semi-persistent scheduling is employed.

BACKGROUND

Universal Mobile Telecommunications System (UMTS) is an example of amobile radio communications system. UMTS is a 3rd Generation (3G) mobilecommunication system employing Wideband Code Division Multiple Access(WCDMA) technology standardized within the 3^(rd) Generation PartnershipProject (3GPP). In the 3GPP release 99, the radio network controller(RNC) in the radio access network controls radio resources and usermobility. Resource control includes admission control, congestioncontrol, and channel switching which corresponds to changing the datarate of a connection. Base stations, called node Bs (NBs), which areconnected to an RNC, orchestrate radio communications with mobile radiostations over an air interface. RNCs are also connected to nodes in acore network, i.e., Serving GPRS Support Node (SGSN), Gateway GPRSSupport Node (GGSN), mobile switching center (MSC), etc. Core networknodes provide various services to mobile radio users who are connectedby the radio access network such as authentication, call routing,charging, service invocation, and access to other networks like theInternet, public switched telephone network (PSTN), Integrated ServicesDigital Network (ISDN), etc.

The Long Term Evolution (LTE) of UMTS is under development by the 3rdGeneration Partnership Project (3GPP) which standardizes UMTS. There aremany technical specifications hosted at the 3GPP website relating toEvolved Universal Terrestrial Radio Access (E-UTRA) and EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN), e.g., 3GPP TS36.300. The objective of the LTE standardization work is to develop aframework for the evolution of the 3GPP radio-access technology towardsa high-data-rate, low-latency and packet-optimized radio-accesstechnology. In particular, LTE aims to support services provided fromthe packet switched (PS)-domain. A key goal of the 3GPP LTE technologyis to enable high-speed packet communications at or above about 100Mbps.

FIG. 1 illustrates an example of an LTE type mobile communicationssystem 10. An E-UTRAN 12 includes E-UTRAN NodeBs (eNBs) 18 that provideE-UTRA user plane and control plane protocol terminations towards theuser equipment (UE) terminals 20 over a radio interface. An eNB issometimes more generally referred to as a base station, and a UE issometimes referred to as a mobile radio terminal or a mobile station. Asshown in FIG. 1, the base stations are interconnected with each other byan X2 interface. The base stations are also connected by an S1 interfaceto an Evolved Packet Core (EPC) 14 which includes a Mobility ManagementEntity (MME) and to a System Architecture Evolution (SAE) Gateway. TheMME/SAE Gateway is shown as a single node 22 in this example and isanalogous in many ways to an SGSN/GGSN gateway in UMTS and in GSM/EDGE.The S1 interface supports a many-to-many relation between MMEs/SAEGateways and eNBs. The E-UTRAN 12 and EPC 14 together form a Public LandMobile Network (PLMN). The MMEs/SAE Gateways 22 are connected todirectly or indirectly to the Internet 16 and to other networks.

To provide efficient resource usage, LTE and other systems that usedshared radio resources support fast “dynamic” scheduling where resourceson the shared channels, e.g., in LTE this includes the physical downlinkshared channel (PDSCH) and the physical uplink shared channel (PUSCH),are assigned dynamically to user equipment (UE) terminals and radiobearers on a sub-frame basis according to the momentary traffic demand,quality of service (QoS) requirements, and estimated channel quality.This assignment or scheduling task is typically performed by one or moreschedulers situated in the eNB.

The overall scheduling concept for the downlink is illustrated in FIG.2. To support fast channel-dependent link adaptation and fastchannel-dependent time and frequency domain scheduling, the UE 20 may beconfigured to report the Channel Quality Indicator (CQI) to aid the eNB18 in its dynamic scheduling decisions. Typically, the UE 18 bases theCQI reports on measurements on downlink (DL) reference signals. Based onthe CQI reports and QoS requirements of the different logical channels,the DL scheduler in the eNB 18 dynamically assigns time and frequencyradio resources, i.e., scheduling blocks. The dynamically-scheduledradio resource assignment is signaled on the Physical Downlink ControlChannel (PDCCH) in the LTE example. Each UE 20 monitors the controlchannel to determine if that UE is scheduled on the shared channel(PDSCH in LTE), and if so, what physical layer radio resources to findthe data scheduled for downlink transmission.

The uplink scheduling concept is illustrated in FIG. 3. The UE 20informs the UL scheduler in the eNB 18 when data arrives in the transmitbuffer with a Scheduling Request (SR). The UL scheduler selects thetime/frequency radio resources the UE will use and also selects thetransport block size, modulation, and coding because link adaptation forthe uplink is performed in the eNB. The selected transport format issignaled together with information on the user ID to the UE. This meansthat the UE must use a certain transport format and that the eNB isalready aware of the transmission parameters when detecting the UL datatransmission from that UE. The assigned radio resources and transmissionparameters are sent to the UE via the PDCCH in LTE. Later, additionalScheduling Information (SI) such as a Buffer Status Report (BSR) or apower headroom report may be transmitted together with data.

Although dynamic scheduling is the baseline for LTE and other systems,it can be less than optimum for certain types of services. For example,for services such as speech (VoIP) where small packets are generatedregularly, dynamic scheduling results in substantial control signalingdemands because a radio resource assignment needs to be signaled in eachscheduling instance, which in the case of VoIP, an assignment must besignaled for every VoIP packet. To avoid this high relative signalingoverhead for these types of services, resources may be assignedsemi-statically, which is called “semi-persistent” or “persistent”scheduling. A semi-persistent assignment is only signaled once and isthen available for the UE at regular periodic intervals without furtherassignment signaling.

Many modern wireless communications systems use a hybrid ARQ (HARQ)protocol with multiple stop-and-wait HARQ “processes”. The motivationfor using multiple processes is to allow continuous transmission, whichcannot be achieved with a single stop-and-wait protocol, while at thesame time having some of the simplicity of a stop-and-wait protocol.Each HARQ process corresponds to one stop-and-wait protocol. By using asufficient number of parallel HARQ processes, a continuous transmissionmay be achieved.

FIG. 4 shows an eNB 18 with an HARQ controller 22 that includes multipleHARQ entities 1, 2, . . . , m (24), with each HARQ entity managing HARQprocesses for a corresponding active UE 1, 2, . . . , n (20). FIG. 5shows each HARQ entity 24 managing one or more HARQ processes A, B, . .. , n (26). One way of looking at the HARQ process is to view it as abuffer. Each time a new transmission is made in an HARQ process, thatbuffer is cleared, and the transmitted data unit is stored in thebuffer. For each retransmission of that same data unit, the receivedretransmitted data unit is soft-combined with the data already in thebuffer.

FIG. 6 illustrates an example of the HARQ protocol where P(X,Y) refersto the Yth transmission in HARQ process X. The example assumes six HARQprocesses. If a large number of higher layer packets (e.g. IP packets)are to be transmitted, for each transmission time interval (TTI), theRLC and MAC protocol layers perform segmentation and/or concatenation ofa number of packets such that the payload fits the amount of data thatcan be transmitted in a given TTI. The example assumes for simplicitythat one IP packet fits into a TTI when RLC and MAC headers have beenadded so that there is no segmentation or concatenation.

Packets 1 through 6 can be transmitted in the first six TTIs in HARQprocesses 1 through 6. After that time, HARQ feedback for HARQ process 1is received in the receiver. In this example, a negative acknowledgment(NACK) for HARQ process 1 is received, and a retransmission is performedin HARQ process 1 (denoted P1,2). If a positive acknowledgment (ACK) hadbeen received, a new transmission could have started carrying packet 7.If all 6 first transmissions failed (i.e., only NACKs are received),then no new data can be transmitted because all HARQ processes areoccupied with retransmissions. Once an ACK is received for an HARQprocess, new data can be transmitted in that HARQ process. If only ACKsare received (no transmission errors), then the transmitter cancontinuously transmit new packets.

In modern cellular systems, synchronous HARQ may be used for the uplinkand asynchronous HARQ for the downlink. For that case, in the uplink,the subframe or transmission time interval (TTI) when the retransmissionoccurs is known at the base station receiver, while for the downlink,the base station scheduler has the freedom to choose the subframe or TTIfor the retransmission dynamically. For both uplink and downlink, asingle-bit HARQ feedback (ACK/NACK) is sent providing feedback about thesuccess of the previous data unit transmission.

A problem created by introducing semi-persistent scheduling, as iscurrently proposed for LTE for example, is that a receiving UE cannotmatch-up a dynamically-scheduled retransmission of a HARQ process withthe initially-transmitted HARQ process that was semi-persistentlyscheduled. If HARQ is operated in asynchronous mode, as is currentlyproposed for example in the LTE downlink, the problem is how the HARQprocesses should be selected for semi-persistent scheduling. After asemi-persistent assignment, both the HARQ transmitter entity as well asthe HARQ receiver entity would, for example, randomly pick an idle HARQprocess with potentially different HARQ process IDs. The reason is thatthe eNB does not send an explicit assignment referring to a particularHARQ process ID. If the HARQ receiver can decode the information, itdelivers the information to higher layers and acknowledges thereception. But if decoding fails, then the HARQ receiver sends anegative acknowledgement, and the HARQ transmitter issues aretransmission of that HARQ process. If the retransmission is scheduleddynamically (as in the LTE downlink), then the corresponding dynamicassignment must contain the identifier of the HARQ process. It is likelythat the HARQ transmitter chose a HARQ process ID for the initialtransmission that was different from the HARQ process ID selected by theHARQ receiver. Consequently, the HARQ receiver cannot match thedynamically retransmitted HARQ process unambiguously to a pending HARQprocess. In fact, there may be multiple pending processes (persistentlyor dynamically scheduled) for which the receiver may not even havereceived the assignment. If different HARQ processes are used by thetransmitter and the receiver, then the data may be erroneouslysoft-combined with other data and the transmitted can not correctlyidentify the HARQ ACK/NACK sent for the data. The failure to make thismatch thus significantly increases error rate and decreases throughput.

SUMMARY

Data units are communicated between radio stations over a radiointerface. A radio communications link is established between the radiostations, and a semi-persistent radio resource is allocated to supportdata transmission over the communications link. The semi-persistentradio resource is associated with a corresponding automatic repeatrequest (ARQ) process identifier. Non-limiting examples of asemi-persistent radio resource include a regularly scheduledtransmission time interval, frame, subframe, or time slot during whichto transmit a data unit over the radio interface using an assigned radioresource in the frequency or code domain. Retransmission is requested ofa data unit transmitted using the semi-persistent radio resource. TheARQ process identifier associated with the semi-persistent resource isused to match a retransmission of a data unit dynamically scheduled onthe communications link with the requested data unit retransmission. Ina preferred example embodiment, the ARQ identifier is a hybrid ARQ(HARQ) identifier, where a retransmitted data unit is combined with apreviously-received version of the data unit, and where the HARQidentifier is associated with a HARQ process.

In one non-limiting example embodiment, the semi-persistent radioresource may be associated with multiple corresponding automatic repeatrequest (ARQ) process identifiers.

The association between the semi-persistent radio resource and thecorresponding automatic repeat request (ARQ) process identifier may becommunicated in a number of ways. One example is using a configurationmessage, and another is using a scheduling assignment message.

The technology in this application finds particularly advantageousapplication to communications between a base station and a userequipment (UE). For example, a base station includes a resource managerthat allocates a semi-persistent radio resource for the radioconnection, transmitting circuitry for transmitting data units to the UEusing the semi-persistent radio resource, receiving circuitry to receivea request from the UE to retransmit one of the data units transmittedusing the semi-persistent radio resource, and a processor thatfacilitates retransmission of the one data unit using a radio resource,(different from the semi-persistent radio resource), that is dynamicallyscheduled by the resource manager. The resource manager associates thesemi-persistent radio resource with a corresponding hybrid automaticrepeat request (HARQ) identifier and provides that association to the UEso as to permit the UE to use the HARQ identifier to determine anidentity of retransmitted data unit. In one example embodiment, the HARQidentifier is a HARQ process identifier.

The user equipment (UE) includes receiving circuitry for receiving fromthe base station information indicating that a semi-persistent radioresource is allocated to support data transmission from the base stationover the radio connection. Thereafter, the UE receives data unitstransmitted using the semi-persistent radio resource. The UE alsoreceives from the base station an association between thesemi-persistent radio resource and a corresponding hybrid automaticrepeat request (HARQ) process. Preferably, the UE stores thatassociation. The UE stores information received in the semi-persistentradio resource in the HARQ process associated with that resource. Atransmitter sends a message to the base station requestingretransmission of the data unit associated with the HARQ process andpreviously transmitted using the semi-permanent radio resource if itdetects a transmission error. Processing circuitry, e.g., in the UE,associates a received retransmission of a data unit dynamicallyscheduled on the radio connection with the corresponding pending HARQprocess based on the HARQ process ID signaled in the dynamic resourceallocation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a function block diagram of an example LTE mobile radiocommunication system;

FIG. 2 is a conceptual illustration of downlink scheduling and relatedoperations;

FIG. 3 is a conceptual illustration of uplink scheduling and relatedoperations;

FIG. 4 is a function block diagram showing a non-limiting example of anHARQ controller in an eNB with multiple HARQ entities that correspond tomultiple UEs;

FIG. 5 is a function block diagram showing a non-limiting example of anHARQ entity with multiple HARQ processes;

FIG. 6 shows a non-limiting example of multiple operating HARQprocesses;

FIGS. 7 and 8 are timing diagrams illustrating the problem where the UEand eNB in some situations can end up using the same HARQ process;

FIG. 9 is a diagram illustrating communication over a radio link betweentwo radio stations;

FIG. 10 is a flow chart diagram illustrating non-limiting, exampleprocedures in which dynamically-scheduled retransmissions of data unitsthat were initially transmitted using semi-persistent radio resourcescan be identified by the receiving radio station;

FIG. 11 is a non-limiting, example function block diagram of a basestation and a UE employing procedures similar to those outlined in FIG.11; and

FIG. 12 is a non-limiting illustrative example.

DETAILED DESCRIPTION

In the following description, for purposes of explanation andnon-limitation, specific details are set forth, such as particularnodes, functional entities, techniques, protocols, standards, etc. inorder to provide an understanding of the described technology. Forexample, much of the description below is provided in the context of anLTE application. But the technology described is not limited to LTE. Inother instances, detailed descriptions of well-known methods, devices,techniques, etc. are omitted so as not to obscure the description withunnecessary detail.

It will be appreciated by those skilled in the art that block diagramsherein can represent conceptual views of illustrative circuitryembodying the principles of the technology. Similarly, it will beappreciated that any flow charts, state transition diagrams, pseudocode,and the like represent various processes which may be embodied incomputer readable medium and so executed by a computer or processor,whether or not such computer or processor is explicitly shown. Thefunctions of the various elements including functional blocks may beprovided through the use of dedicated electronic hardware as well aselectronic circuitry capable of executing computer program instructionsin association with appropriate software.

It will be apparent to one skilled in the art that other embodiments maybe practiced apart from the specific details disclosed below. Allstatements reciting principles, aspects, and embodiments, as well asspecific examples, are intended to encompass both structural andfunctional equivalents. Such equivalents include both currently knownequivalents as well as equivalents developed in the future, i.e., anyelements developed that perform the same function, regardless ofstructure.

As explained in the background, the HARQ operation in an LTE type systemcan be either asynchronous, where the HARQ process used fortransmissions and retransmissions is explicitly signaled on a controlchannel, or synchronous, where the HARQ process is not explicitlysignaled, but instead the HARQ process is tied to the timing of thetransmission, e.g., to a system frame number. The benefit with asynchronous protocol is that out-of-band signaling is not needed toidentify the HARQ process associated with a (re)transmitted data unit.This is particularly important in the uplink where it is costly in termsof power to achieve a high reliability on the control channel signaling.

The main mode of operation for the downlink scheduler is dynamicscheduling, where the base station transmits scheduling assignments tothe UEs, based on current conditions, needs, and resources, to indicatewhich radio resources the UEs have been allocated for uplinktransmission and downlink reception. A dynamically scheduled resourcedoes not persist, i.e., does not remain allocated to a UE, after thescheduled transmission is over. The base station also indicates how adata transmission is to be coded and modulated in both uplink anddownlink. For the downlink, where asynchronous HARQ is assumed for anexample embodiment, the HARQ process identifier and redundancy versionmay be included on the control channel, e.g., the L12 control channel,together with the dynamic scheduling assignment.

In the downlink, because the HARQ protocol is asynchronous, a data unitretransmission may occur at any time after the NACK feedback has beenreceived in the base station transmitter. Thus, there is a need toidentify the HARQ process for which the transmission is made in orderfor the UE's HARQ receiver to correctly combine a transmission with thecorrect retransmission. This is done by indicating the HARQ process inthe scheduling assignment on a control channel, like the PDCCH, both forthe initial dynamically-scheduled transmission and subsequentdynamically-scheduled retransmissions.

A problem with semi-persistent scheduling is that there is no schedulingassignment before each transmission/retransmission that provides theHARQ process identity of the transmitted unit sent via thesemi-persistent resource. But the HARQ receiver still must match dynamicretransmissions of a data unit, e.g., a MAC PDU, with the persistentlyscheduled first HARQ transmission of the same data unit.

For a semi-persistently allocated resource, the eNodeB does not send adynamic assignment message, and thus, cannot request a particular HARQprocess to be used for the initial transmission of a data unit.Therefore, the eNodeB randomly selects one of its idle HARQ processesand uses it to prepare and transmit a data unit using thesemi-persistently assigned transmission resource. The UE also randomlyselects an idle HARQ process and prepares to receive and decode dataexpected from the eNB. If the UE can decode the initial transmissionfrom the eNodeB, then there is no problem. But if the UE must request aretransmission, then the eNodeB sends a dynamically scheduled downlinkassignment indicating the resource, modulation scheme, transport format,and the HARQ process ID for the retransmission. When the UE receivesthis assignment, the indicated HARQ process ID very likely does notmatch the identifier of the randomly chosen process the UE used forinitial reception.

In certain scenarios and under certain preconditions the UE couldidentify such a dynamic resource assignment and match it to the HARQprocess used for reception of the semi-persistent allocation. However,(1) if multiple processes are used in parallel, (2) if the eNodeB doesnot schedule the retransmission after exactly one round trip time (RTT)period, or (3) if a previous dynamic resource assignment was lost,(these are three examples), the mapping is likely to be wrong, leadingto a loss of the data unit.

FIG. 7 depicts an example of a problem where the UE and eNB in somesituations can end up using the same HARQ process. In FIG. 7, there aresix transmission time intervals (TTIs), and the repeat period for a TTIis indicated as 1 round trip time (RTT). The dashed boxes indicatetransmissions, first transmissions in the HARQ processes 1, 5 and 2 areindicated by the numbers 1, 5, and 2 respectively. Retransmissions inthe same processes are indicated by 1′, 5′, and 2′. Note that thetransmitter in asynchronous HARQ is not restricted to using the HARQprocess in any given order. The eNB makes a semi-persistent transmissionduring TTI 6 indicated by a question mark (?) because the HARQ processidentity is not known by the UE. When the HARQ retransmission for thisHARQ process (indicated by 4′) is made, i.e. the UE received ascheduling assignment indicating a HARQ retransmission for HARQ process4, the UE can conclude that this retransmission must belong to thetransmission marked with the question mark since in this special casethere is no other HARQ process outstanding. So it is possible for the UEto correctly combine a retransmission with a transmission done in asemi-persistent resource, but only if the HARQ processor in the UE keepstrack of the all the HARQ process IDs being used. In the example in FIG.7, because no other HARQ process has been negatively acknowledged by theUE, a dynamic downlink assignment indicating a retransmission for theprocess with HARQ process ID 4 must correspond to the expectedretransmission of the data unit associated with the semi-persistentassignment.

But in many cases it will not be possible for the UE to determine whichHARQ process ID the eNB used for a transmission. FIG. 8 shows the casewhere the eNB intended to transmit dynamically scheduled data in HARQprocess 4 (indicated by the number 4), but the scheduling assignment wasnot received by the UE. When the UE receives the scheduling assignmentfor the retransmission of HARQ process 4 (indicated by 4′), the UE triesto combine this retransmission with the semi-persistent transmissionindicated by a question mark. The result is a combination of twodifferent data units that ultimately results in excessive delay.

To overcome these difficulties, each semi-persistent resource allocationis associated with a particular HARQ process. The eNodeB includes anidentifier of the associated HARQ process in a message it sends to theUE. For example, that message could be a configuration message, (e.g., aradio resource control (RRC) configuration message), that configures thesemi-persistent allocation of transmission (or reception) radioresources. Alternatively, the association may be conveyed along with ascheduling assignment message or some other suitable message.

The HARQ receiver, e.g., the UE in the example where asynchronous HARQis used in the downlink, stores that association. As a result, the HARQreceiver can determine if the HARQ process identifier for a dynamicallyscheduled HARQ retransmission corresponds to the HARQ process identifierfor an initially transmitted data unit sent via a semi-persistentresource, i.e., sent without a resource scheduling assignment.

FIG. 9 is a general diagram illustrating communication over a radio linkbetween two radio stations 1 and 2. Although the technology described asparticular application in cellular radio communications between a basestation and a user equipment (UE), the technology also may be applied inany radio communication between radio stations that employ an ARQ-typeprotocol, semi-persistent resource allocation, and dynamically-scheduledretransmissions of data units.

FIG. 10 is a flowchart diagram illustrating non-limiting exampleprocedures in which dynamically-scheduled retransmissions of data unitsthat were initially transmitted using semi-persistent radio resourcescan be identified by the receiving radio station. In step S1, a radioconnection is established between two radio stations 1 and 2. Asemi-persistent radio resource is allocated to transmit data units overthe radio connection (step S2). The semi-persistent resource isassociated with an ARQ process for this connection (step S3). If thereis a need for more than one semi-persistent process for a radioconnection, then the association can be established with multiple ARQprocesses. The receiving radio station requests a retransmission of oneof the transmitted data units, and the transmitting radio stationretransmits the data unit using a dynamically scheduled radio resource(step S4). The receiving radio station uses that association previouslyestablished in step S3 to determine what data unit has been dynamicallyretransmitted by the transmitting radio station (step S5).

FIG. 11 is a non-limiting, example function block diagram of a basestation and a UE employing procedures similar to those to outlined inFIG. 10. A base station communicates over a radio interface indicated atthe dash line 58 with a UE. The base station includes a controller, andinterface 42 for connection to one or more other nodes and/or networks,a buffer manager 44 including multiple UE buffers 46, a resource manager48 including uplink scheduler 50 and downlink scheduler 52, an HARQprocessor 54, and a transceiver 56. The controller 40 is responsible forthe overall operation of the base station. Although the radio resourcesare described here in terms of TTIs, frames, sub-frames, or as timeslots during which a data unit may be transmitted over the radiointerface, it is to be understood that other types of radio resourcesmay also be allocated including for example different frequencies and/ordifferent orthogonal subcarriers as is the case in orthogonal frequencydivisional multiplexing (OFDM).

The buffer manager 44 includes logic for directing user data into andout of an appropriate queue or buffer 46. Each of the buffers 46 isassociated with a respective radio connection to a UE and stores userdata destined for transmission on the downlink over the air interface 56to the respective UE. Data from the UE buffers is assembled into atransmission data unit and provided to the transceiver 56 fortransmission using an appropriate radio resource to the appropriate UE.Those radio resources are managed by the radio resource manager 46. Thetransceiver 46 can comprise conventional elements such as suitableencoder(s), amplifier(s), antenna(s), filter(s), conversion circuitry,etc. The uplink scheduler 50 is responsible for providing dynamic radioresource grants to the various UEs that need to transmit data units inthe uplink to the base station. The downlink scheduler 52 is responsiblefor scheduling dynamic radio resource assignments from the base stationto the various UEs as well as establishing semi-persistent radioresource allocations where appropriate, e.g., to support services suchas voice over IP that benefit from semi-persistent resource allocation.The HARQ processor 54 is responsible for managing HARQ processes and mayinclude multiple HARQ entities such as those described in conjunctionwith FIGS. 4 and 5.

The UE at the bottom of FIG. 11 includes a supervisory controller 70, aradio transceiver 62, a resource allocation memory 64, a buffer manager70 with one or more UE buffers, and a HARQ processor 74. The HARQprocessor 74 manages the HARQ process(es) being employed by the UE. TheUE buffer(s) 70 stores the data units that are to be transmitted via thetransceiver 62 using an appropriately-allocated radio resource. Theresource allocation memory allocation memory includes schedulinginformation 66 received from the uplink and downlink schedulers 50 and52 from the base station. Resource allocation memory 64 also stores oneor more associations between semi-persistent resource allocations andHARQ processes 68. The HARQ processor 74 uses these stored associationsin order to match the HARQ process for a dynamically scheduled,retransmitted data unit with the HARQ process for a data unit that wasinitially transmitted using a semi-persistent radio resource. Once theHARQ processes are properly matched by the UE, the HARQ processor 74 maysoft-combine different redundancy versions of the same data unit as partof decoding that data unit.

FIG. 12 is an illustration to demonstrate one example of how thistechnology could work in practice. A semi-persistent assignment, shownas an arrow (A) pointing to a hatched lined block, is set for subframeor TTI 3 and repeats 20 TTIs later at TTI 23, wherein in this simpleexample, each TTI is assumed to be 1 msec. That semi-persistentscheduling assignment is configured via higher level signaling, e.g., anRCC reconfiguration message, with a certain period or cycle, which inthe case of voice over IP (VoIP) might be a period of 20 msec. Thus, TTI3, TTI 3+N (where in this non-limiting VoIP example, N equals 20 msec),TTI 3+2 N, TTI 3+3N, etc. are the semi-persistent assigned resources fora downlink UE transmission. The semi-persistent resource assignment mayalso be conveyed to the UE by a message sent over a control channel,e.g., the PDCCH, indicating that the assignment is semi-persistent. Thecontrol channel approach is assumed in this example. Once thissemi-persistent assignment is received by the UE, the UE is scheduledone every 20 msec to receive a data unit from the base station until thesemi-persistent assignment is revoked by the base station. As a result,no additional scheduling assignment is needed during a VoIP burst. Thus,there is no scheduling assignment message received on the PDCCH(indicated by an arrow pointing downwards in FIG. 13) for TTI 23, whichis indicated at (B).

In conjunction with the semi-persistent resource assignments, the basestation is also transmitting dynamic scheduling assignments. Dynamicallyscheduled assignments are shown in FIG. 12 at TTIs 10, 11, and 12indicated by the three downward arrows labeled as (C) pointing to solidblack blocks. In this simple example, each scheduling assignmentschedules one data unit in an HARQ process that is identified in thedynamic scheduling assignment. The data unit transmissions in TTIs 10,11, and 12 are allocated HARQ processes 1, 2, and 3, respectively.

Assume that the HARQ process 0 was associated with the semi-persistentassignment TTI 3 indicated at (A). That association is provided to theUE which stores the association between the semi-persistent resource TTI3+N*20 ms, where N=0, 1, 2, . . . , and the HARQ process 0. Theillustration in FIG. 13 assumes that the base station sends a VoIP dataunit during the semi-persistent TTI 3 and that the UE does not receiveit correctly. As a result, the UE sends a NACK back to the base station.After receiving that NACK, the base retransmits that same VoIP data unitduring dynamically scheduled TTI 22 as indicated by the downward arrowat (D). Thereafter, the next VoIP packet is then transmitted in TTI 23as indicated at (B).

Fortunately, the UE knows that the semi-persistent resource TTI 3 andthe HARQ process 0 are associated because the UE stored that associationinformation earlier. That way, when the UE receives the dynamicallyscheduled data unit at TTI 22 (indicated at (D)), along with the HARQprocess 0 identifier, the UE knows that the data unit received isactually the retransmission of the HARQ process 0 data unit initiallysent at TTI 3. Because of that association, the UE knows that the HARQprocess 0 corresponds to the data unit sent during TTI 3.

In one non-limiting example embodiment, the allocation of HARQ processidentifiers for the semi-persistent allocation can be restricted toprocess identifiers that are not used for dynamic scheduling of data.For example, if there are a total of HARQ processes, dynamic schedulingmight use HARQ process identifiers 1 . . . 6 and the semi-persistentallocations can be made with HARQ process identifiers 7 and 8.

In summary, the technology described above allows asynchronous HARQ tobe used in a reliable way for semi-persistent scheduling, increases thethroughput, and minimizes the error cases for semi-persistentscheduling.

None of the above description should be read as implying that anyparticular element, step, range, or function is essential such that itmust be included in the claims scope. The scope of patented subjectmatter is defined only by the claims. The extent of legal protection isdefined by the words recited in the allowed claims and theirequivalents. All structural and functional equivalents to the elementsof the above-described preferred embodiment that are known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the present claims. Moreover, itis not necessary for a device or method to address each and everyproblem sought to be solved by the present invention, for it to beencompassed by the present claims. No claim is intended to invokeparagraph 6 of 35 USC §112 unless the words “means for” or “step for”are used. Furthermore, no embodiment, feature, component, or step inthis specification is intended to be dedicated to the public regardlessof whether the embodiment, feature, component, or step is recited in theclaims.

1. A method for communicating data units between radio stations over aradio interface, where a radio communications link is establishedbetween the radio stations and a semi-persistent radio resource isallocated to support data transmission over the communications link, themethod being characterized by: associating the semi-persistent radioresource with a corresponding automatic repeat request (ARQ) processidentifier; requesting retransmission of a data unit transmitted usingthe semi-persistent radio resource, where the data unit is retransmittedusing a dynamically scheduled radio resource that is different from thesemi-persistent radio resource; and using the ARQ process identifierassociated with the semi-persistent resource to match a retransmissionof a data unit dynamically scheduled on the communications link with therequested data unit retransmission.
 2. The method in claim 1, whereinthe ARQ process identifier is a hybrid ARQ (HARQ) identifier and aretransmitted data unit is combined with a previously-received versionof the data unit.
 3. The method in claim 2, wherein the HARQ identifieridentifies a HARQ process.
 4. The method in any of the preceding claims,wherein the semi-persistent radio resource includes a transmission timeinterval, frame, subframe, or time slot during which to transmit a dataunit over the radio interface.
 5. The method in any of the precedingclaims, further comprising associating the semi-persistent radioresource with multiple corresponding automatic repeat request (ARQ)process identifiers.
 6. The method in claim 1, further comprisingcommunicating the association between the semi-persistent radio resourceand the one or more corresponding automatic repeat request (ARQ) processidentifiers using a configuration message.
 7. The method in claim 1,further comprising communicating the association between thesemi-persistent radio resource and the one or more correspondingautomatic repeat request (ARQ) process identifiers using a schedulingassignment message.
 8. The method in claim 1, wherein the radio stationsinclude a base station and a user equipment.
 9. Base station equipmentfor communicating data units with a user equipment (UE) over a radioconnection established between the base station and the UE, comprising:a resource manager configured to allocate a semi-persistent radioresource for the radio connection; transmitting circuitry fortransmitting data units to the UE using the semi-persistent radioresource; receiving circuitry configured to receive a request from theUE to retransmit one of the data units transmitted using thesemi-persistent radio resource; a processor configured to facilitateretransmission of the one data unit using a radio resource dynamicallyscheduled by the resource manager, wherein the base station equipment isfurther characterized by: the resource manager being configured toassociate the semi-persistent radio resource with a corresponding hybridautomatic repeat request (HARQ) identifier and to provide thatassociation to the UE so as to permit the UE to use the HARQ identifierto determine an identity of retransmitted data unit.
 10. The basestation equipment in claim 9, wherein the HARQ identifier is a HARQprocess.
 11. The base station equipment in claim 10, whereinsemi-persistent radio resource includes a transmission time interval,frame, subframe, or time slot during which to transmit a data unit overthe radio connection.
 12. The base station equipment in claim 10,wherein the resource manager is configured to associate thesemi-persistent radio resource with multiple corresponding HARQprocesses.
 13. The base station equipment in claim 10, wherein thetransmitting circuitry is configured to transmit the association betweenthe semi-persistent radio resource and the corresponding HARQ processusing a configuration message.
 14. The base station equipment in claim10, wherein the transmitting circuitry is configured to transmit theassociation between the semi-persistent radio resource and thecorresponding HARQ process using a scheduling assignment message.
 15. Auser equipment (UE) for communicating data units with a base station(18) over a radio connection established between the UE and the basestation, comprising: receiving circuitry configured to receive from thebase station information indicating that a semi-persistent radioresource is allocated to support data transmission from the base stationover the radio connection, and thereafter, to receive data unitstransmitted using the semi-persistent radio resource; the UE beingcharacterized by: the receiving circuitry being configured to receivefrom the base station an association between the semi-persistent radioresource and a corresponding hybrid automatic repeat request (HARQ)process; transmitting circuitry configured to send a message to the basestation requesting retransmission of a data unit that was previouslytransmitted using the semi-persistent radio resource; and processingcircuitry configured to use the HARQ process associated with thesemi-persistent resource to identify a received retransmission of a dataunit dynamically scheduled on the radio connection with the requesteddata unit retransmission.
 16. The UE in claim 15, whereinsemi-persistent radio resource includes a transmission time interval,frame, subframe, or time slot during which to transmit a data unit overthe radio interface.
 17. The UE in claim 15, wherein the receivingcircuitry is configured to receive from the base station an associationbetween the semi-persistent radio resource and multiple correspondingHARQ processes.
 18. The UE in claim 15, wherein the receiving circuitryis configured to receive from the base station a scheduling assignmentmessage that includes the association between the semi-persistent radioresource and the one or more corresponding HARQ processes.
 19. The UE inclaim 15, wherein the receiving circuitry is configured to receive fromthe base station a configuration message that includes the associationbetween the semi-persistent radio resource and the one or morecorresponding HARQ processes.
 20. The UE in claim 15, further comprisingmemory for storing the association between the semi-persistent radioresource and one or more corresponding hybrid automatic repeat request(HARQ) processes.